This invention relates to a coil device which constitutes a winding component such as a choke coil and a transformer.
FIGS. 9(a), (b), (c) and (d) are illustrations showing an example of a conventional coil and its assembly. The conventional coil 1, as shown in (a) and (b) of FIG. 9, has a coil 4 which is formed by providing a winding 3 on a body portion 2b of a drum core 2 having flanges 2a, 2a on its opposed ends and, as shown in (c) and (d) of FIG. 9, a terminal 9, of synthetic resin is prepared by embedding two terminal elements 8, 8 in a base seat 5. The coil 4 is mounted on a circular, coil holding portion 6 on a central portion of the base seat 5, and fixed thereto by an adhesive agent or the like.
Further, as shown in FIGS. 10(a) and (b), the terminal elements 8, 8 of the terminal 9 is formed with a crank-shaped lead frame which has a wrapping portion 8a for connection with an end of the coil 4 and a mounting portion 8b which is exposed at a back surface of the terminal 9. In general, the lead frame described above is embedded in a terminal fixing portion 7 which is projected from an end portion of the base seat 5 by means of an insert molding technique.
Many attempts have been made for miniaturization and thickness reduction of the electronic devices for meeting with the requirements of miniaturization and thickness reduction in each of the electronic elements and components for the devices. In the circumstances as described above, there are several inconveniences and problems to be solved with respect to a further miniaturization and thickness reduction in the coil device.
Firstly, a total height of the coil device is determined by a thickness of the coil and a height of a mounting surface of the coil on a base seat, and therefore it would be effective to reduce the height of the core for the purposes of thickness reduction. However, in the case of a drum core 2 of the structure described above, a middle portion of a tubular core of magnetic material is cut out to form a bobbin shaped structure as shown in FIG. 9(a) and, therefore, it is quite difficult from the viewpoint of the cutting processing technique to extensively reduce the thickness xe2x80x9caxe2x80x9d and the dimension of a winding portion xe2x80x9cbxe2x80x9d of a flange 2a. In formation of the core, the cutting process of the middle portion of the tubular body as described above requires an extremely high precision technique, with the result being reduced productivity.
Secondly, the terminal elements 8 in the conventional prior art coil device has a structure in which opposed ends of a lead frame are embedded into mold resin as shown in FIG. 10, and this causes a reduction of the area of a resin fixture portion (that is, an embedding portion of the terminal elements 8 at a terminal fixture portion 7) with the advance of miniaturization of the terminal 9, and thus the fixing strength for the terminal elements 8 is lowered and consequently the terminal elements likely fall out, resulting in a loss of reliability.
It is, therefore, an object of the present invention to provide, in view of the above situation, a coil device in which the height of a winding component can be reduced without sacrificing practical usability thereof.
Another object of the present invention is to provide a new coil device, which permits adaptability to the recent trend of miniaturization and thickness reduction of electronic appliances.
A further object of the present invention is to provide a new coil device, which provides improvement in electromagnetic properties and reliability.
According to one aspect of the present invention, there is essentially provided a coil device comprising a coil composed of a core and a winding on the core, and a terminal having a base seat for holding the coil and terminal elements. The coil device has a flange on one side of the core, and no flange is provided on the other side of the core.
In the one-sided flange structure described above, formation can be made by using a mold without using a cutting processing technique, so that the flange can be made thinner in contrast to a flange formed with the cutting technique applied in the conventional prior art. Thus, a reduction in the height of the core can be realized.
In a preferred embodiment, the terminal has a coil retaining space (hole or recess) for securing therein a body portion of the core. This will permit easy positioning of the coil and improved assembly efficiency. Further, since a marginal space for assembly is permitted in a height direction, dispersion of height in a core production can be absorbed in the assembly procedure, so that the dimensional allowance can be increased.
In a further embodiment, the base seat has a projected rim at its circumferential end so that the projected rim overlaps the coil. Further, the base seat is made of a mixture of a synthetic resin material and a magnetic material. This permits the formation of a closed magnetic circuit by combining the projected rim of the base seat and the flange of the core, so that magnetic leakage of the coil is reduced to thereby improve the electromagnetic properties.
In an additional preferred embodiment, an opposed end of a one-sided flange core is substituted with a jig, and fusion-bonded wire is wound directly around the body portion of the core. When a winding is applied to the one-sided flange core, a toroidal coil can be inserted or fitted to the body portion of the core. In this embodiment, the fusion-bonded wire is applied directly to the body portion of the core. At the time of winding, the jig (a butt joint jig) for a winding machine is used for the other flange (that is, an xe2x80x9cexcludedxe2x80x9d flange of the one-sided flange of the core) for a winding frame so that winding is made between the excluded flange and the one-sided, existing flange. In the case of the direct winding as described, no clearance is required relative to the body portion of the core as is required in the toroidal coil and, therefore, the space for the clearance can effectively be used such that the winding number can be increased and a dimension of the wire can be increased so that improvement in electromagnetic properties can be obtained. Further, assembly efficiency can be improved relative to the case in which a toroidal coil is used.
In a second aspect of the present invention, there is essentially provided a coil device comprising a coil composed of a core and a winding on the core, and a terminal having a base seat for holding the coil and a terminal element. The base seat has a terminal fitting portion and a terminal element embedded in the terminal fitting portion, and the terminal element has wrapping (or bundling) portions at its ends and a mounting portion at its middle portion. Also, only a widthwise portion of the mounting portion is exposed.
In this structure, the portion to be fixed by the molded resin is extended to thereby increase the fixing strength of the terminal elements. Further, this structure permits visual inspection of the welding condition of the terminal elements from an upper position.
In the second aspect of the invention described above, the mounting portion is exposed at the portion, which is positioned at the same place of the bottom surface of the terminal. This will facilitate further miniaturization and improvement in strength of the terminal elements because of the increase of a molded portion.